Francis henry froedman



\ quired, such as a. base for photographic picthe tidal operation of decolorizing or bleachwater is then added, and finally the alcohol has more fully hereinafter specified.

wise be almost impervious to actinic light and UNITED S ATE PATENT OFFICE."

FRANCIS HENRY FROEDMA'N, or bonus, COUNTY or DUBLIN, inst/inn.

Maison or MANUFACTURING snrroins FOR PHOTOGRAPilIC EMULS|0N.'

SPECIPICATIQNformin'g part of Letters Patent No. 386.006, dated July-l0, 1888.

Application tiled March 17, 1887. sol-taint.

To all whom it may concern.-

B itk now-n that I, FRANCIS HENRY FRQE MAN, of 23 Mary street,'Dublin, Ireland, a citizen' of the United Kingdom of Great Brit-. aim and Ireland, have invented a certain new and useful Manufacture of a Transparent Flexible Material suitable for all purposes where a transparent, flexible, and light material is retures, transparent show-cards, artistic work, and other similar purposes; and I-do hereby declare that thefollowing is a clear and exactdescription of theinvention, which will enable others skilled in the art to which it appertains to make and use the same. I

This invention relates to animproved base will be flexible, insoluble in water, transpar cot, and perfectly permeable to actinic light,

To this end my invention consists in a base composed of gelatine combined with a suitable chromium salt and rendered insoluble in water by exposure to light, and finally bleached by means of sulphurons acid or the salts of snch. acid,-as more fully-hereinafter scliforlh i '2 My inventionl jis particularly designed to produce abase orsheet for photographic nega-= tives, which must necessarily be transparent or permeable to actinic light to permit the negative to be printed therefrom. For this reason ingthebase is absolutely necessary, as the color, of the sheet after exposure would otherutterly worthless for the purpose intended.

In carrying out my invention I employ any of the chromium salts, but preferably the bichromate of potash and any suitable variety of gclatine, the proportions varying according to circumstances. I

Eor general purposes I employ the following ingredients in theproportions named: gelatinc, th ree parts; water, twenty-four parts; bichroniate-of potash, six and one-half parts; alcohol, four parts; glycerine, q. s.

The gelatine is softened by soaking in a portion of the water. It is then heated in a water bath and more of the water is added. The bichromate in solution in the remaining and glycerine, and the whole is stirred until a 231.3%. (No specimens.) Patented in England August 20, 1886, No. 10,659.

homogeneous emulsion is obtained. The emulsion thus prepared maybe formed into sheets in any convenientmanner. In practice, however, Igenerally prepare the sheet by spread ing the same on anJabSoIutely clean flat sur .face suitably prepared for its reception and afterward drying it and removing it from such surface;

I preferably employ perfectly flat glass upon whieh to, prepare the sheets, and proceedas follows: The glass is first cleaned in any convenient'manner and its surface coated witlr 'collodi'on, which is allowed-to set, when the plate is immersed in water until all ap pearance ofgreasiness is removed, or the-surface of the plate maybe coated at its edges with a film of rubber dissolved in benzole,

which is allowed to dry. The biehromated gelatine solution is tlienspreud upon-the preparedplate in any convenient manner and allowed to dry, It is then exposed to light until it becomes insoluble, alter which it is thoroughly washed to remove any undccomposed chrome-salt. ,It is then immersed in a solution 0t"- sulphurous acid, or one of its compounds, and allowed to remain until thoroughly bleached,after which it is removed and washed until all acidity disappears. .It is then dried and the film finallystripped from they glass, when'it is ready for use. The sensitive emulsion is then applied in the manner cmployed by those skilled in the art of making sensitized photographic plates.

Thesensitized sheet may be employed as usual in the ordinary camera dark slide or plate holder, or it may be prepared in suitable lengths and'employed in roller-holders, as will be readily understood by photographers.

Havingthus described my invention, what I clai m,.and desire to secure by Letters Patent, 1s-

The process herein described 01 preparing a base for photographic negatives, the same consisting in forming a sheet of insoluble bichromated'gclati no and decolorizingsaid sheet by means oi sulphur-ens acid, so as to transmit actinic light for the purpose of printing, substantially as specified. Dated Ii ith day of Maw b, 1887.

FRANCIS HENRY FROEDMAN. Witnesses:

ANGELO Flume, Q. E.,

10 Lcinster Street, Dublin. J. L. MOCASKILL. 

